Daughter Elsie derailed locomotive (6)
I believe the answer is:
diesel
'locomotive' is the definition.
(diesel locomotive is a kind of locomotive)
'daughter elsie derailed' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'derailed' indicates anagramming the letters (I've seen this in other clues).
'elsie' anagrammed gives 'iesel'.
'd'+'iesel'='DIESEL'
(Other definitions for diesel that I've seen before include "Rudolf __ , French-born German engine inventor, d.1913" , "Kind of engine" , "Fuel used by heavy vehicles" , "Lorry fuel" , "Derv" .)